Removal of toxic materials from soil and water and the remediation of industrial effluents is a matter of significant economic and environmental concern. Accordingly, significant effort has been expended to develop remediation and detoxification technologies. Likewise, methods to reduce the level of contaminants resulting from industrial chemical processes are being sought. One powerful approach has focused on the use of free-radicals. Free-radicals are typically highly energetic and unstable, and can effect the oxidation or reduction of a broad spectrum of compounds.
The generation of free-radicals by biological systems is known. Research by Koenigs on the action of "Fenton" reagents against cellulose and wood cell wall components suggested that iron and hydrogen peroxide were involved in the production of highly reactive hydroxyl radicals which could initiate the depolymerization of cellulose in wood as: Fe.sup.2+ +H.sub.2 O.sub.2 .fwdarw.Fe.sup.3+ +HO.sup.. +HO.sup.-. "Hydrogen peroxide and iron: a microbial cellulolytic system?" in Cellulose as a Chemical and Energy Resource, Symposium 5, Biotechnology and Bioengineering. Wilke, C. R. (Ed.), John Wiley and Sons, New York 5:151-159 (1975). Hydroxyl radicals can also be generated in the presence of metals by the related Haber-Weiss reaction (Haber and Weiss, Proc. R. Soc., 147:332-351 (1934)) as: O.sub.2.sup.- +H.sub.2 O.sub.2 .fwdarw.O.sub.2 +HO.sup.- +HO.sup... This reaction is now known to occur via the superoxide reduction of iron with hydrogen peroxide oxidation of iron to produce hydroxyl radicals.
Oxalate has been postulated to play a role in direct acid attack upon the wood cellulose and hemicellulose (Shimada et al., 5th Int'l Conf. Biotechn. in the Pulp and Paper Industry, Kyoto, Japan, 273-278 (1992); Green et al., Mater. Org., 26:191-213 (1991)). It has also been suggested that oxalate may function to reduce iron III to iron II which then reacts with H.sub.2 O.sub.2 to yield OH. However, Hyde and Wood, Int'l Res. Group Wood Preservation Series, Stockholm, Sweden, Doc. IRG/WP 95-10104 (1995) and others (Sulzberger and Laubsher, Marine Chem., 50:103-115 (1995); Sedlak and Hoigne, Atmospheric Environment, 27A:2173-2185 (1993); and Zepp et al., Environ. Sci. Technol. 26:313-319 (1992)) have observed that oxalate does not reduce ferric iron except as a light-dependent reaction. Therefore, oxalate cannot function as a direct catalyst of Fenton type chemical reactions in wood.
Wood, FEMS Microbiol. Rev. 13:313-320 (1994) has also investigated pathways for Fenton reagent production in fungi, and Hyde and Wood (Int'l Res. Group Wood Preservation Series, Stockholm, Sweden, Doc. IRG/WP 95-10104 (1995)) have also recently proposed a mechanism for brown rot degradation based on Fenton chemistry and the enzymatic generation of iron species. In their model, a pH dependent autoxidation of Fell is postulated to produce hydrogen peroxide at a distance from the hyphae to initiate Fenton reactions leading to the formation of hydroxyl radicals. However, in the absence of other Fenton chemistry reactants or reactive oxygen species, FeII would not be expected to promote an oxidative degradation of cellulosic compounds found in wood. Kirk et al., Holzforschunq 45, 239-244 (1991). Although other mechanisms for the production of hydrogen peroxide from an oxalic acid oxidase have also been suggested in brown rot fungi (Espejo and Agosin, Appln. Environ. Microbiol., 57:1980-1986 (1991), a mechanism which would adequately explain a site specific reaction of free FeII and hydrogen peroxide within the wood cell wall has not been put forward.
In studies of wood degrading fungi previous researchers have found that through enzymatic action, cation radicals are produced which are responsible for the degradation of various components of the wood cell wall. Backa et al., Holzforschung 46, 61-67 (1992); Barr et al., Arch. Biochem. Biophys. 289:480-485 (1992); and Illman et al., Intl. Res. Group on Wood Preservation, Stockholm, Sweden, Doc. No. IRG/WP/1360 (1988). The pathways for this action, particularly in white rot fungi, have been reviewed by various researchers. Higuchi, T., Wood Sci. and Tech. 24:23-63 (1990) and Tuor et al., J. Biotech. 41:1-17 (1995). Ultimately, however, laboratory duplication of the action of brown and white rot decay fungi via enzymatic action alone has been difficult to achieve. In part this is due to the ephemeral nature of many degradative enzymes from these organisms outside of the immediate extracellular environment of the fungal hyphae.
Brown rot fungi, such as Gloeophyllum trabeum, have been found to secrete extracellular low molecular weight iron binding chelators. Jellison, et al., Appln. Micro. and Biotech., 35:805-809 (1991). It has been demonstrated that these chelators have strong reductive capacity, and can readily reduce the redox potential of FeIII/FeII allowing the chelated iron to be more available for reactions with hydrogen peroxide or other oxidants to produce hydroxyl radicals. Lu, Master of Forestry Thesis, University of Maine, Orono, Me., (August 1994). However, a reasonable explanation for the highly efficient and site-specific oxidation of wood cells by fungi such as G. trabeum has not been put forward.
What is needed in the art is a non-enzymatic means to generate high levels of free-radicals. Further, what is needed is an inexpensive, uncomplicated, low molecular weight redox generating system for penetration into a variety of contaminated matrices. Conversely, a means to protect substrates from biological or non-biological degradation involving free-radical mechanisms is also needed. Quite surprisingly, the present invention provides these and other advantages.